Quench circuit for radiation counter tube



y 1965 E. w. LEAVER ETAL 3,185,847

QUENCH CIRCUIT FOR RADIATION COUNTER TUBE Original Filed April 18, 195?PULSE AMPLIFIER THEIR ATTDRNEY United States Patent Ofi ice 3,l85,84?Patented May 25, 1965 3,185,847 QUENCH CIRCUIT FGR RADIATION COUNTERTUBE Eric W. Leaver and George R. Mounce, Willowdale, Ontario, Canada,assignors to Electronic Associates Limited, a Canadian company Originalapplication Apr. 18, 1957, Ser. No. 653,570, now Patent No. 3,038,606,dated June 12, 1962. Divided and this application Feb. 6, 1962, Ser. No.181,494 2 Claims. (Ci. 25083.6)

This invention relates to a quench circuit for radiation counter tubes.

This application is a division of our copending application Serial No.653,570, filed April 18, 1957, now Patent No. 3,038,606, dated June 12,1962, hereinafter referred to as the parent patent.

Radiation counter tubes, also known in the art as Geiger-Muller tubes,are useful in apparatus for the measurement of physical properties ofmaterials without physically contacting the subject material to bemeasured. For example, in the parent patent there is describedmeasurement apparatus wherein a radiation counter tube is used inapparatus for the measurement of liquid level contained in cans whichare transported at high speed on a conveyor belt. A radiation countertube, when subjected to a sufiiciently high potential between anode andcathode, will generate short duration pulses in response to radiationincident thereon, the higher the intensity of incident radiation thefaster the rate of occurrence of the pulses.

As is well known, Geiger tubes have a life which is limited to a finitenumber of pulses produced, and it is a principal object of the inventionto provide a novel quench circuit which is effective to quench rapidlyeach generated counter pulse to prolong the tube life.

The invention features connection of the radiation counter tube in aregenerative feedback loop of an ampliher. The amplifier is so biased asnormally to be at an extreme of current conduction and in consequence ofamplifier-radiation counter tube interconnections specified ereinafterthe counter tube anode-cathode potential is maintained below thestriking potential of the counter tube. That is, even though radiationmay be incident on the tube, no counter pulses are generated. When it isdesired to generate counter pulses, a gating signal i introduced intothe feedback loop. The gating signal enables generation of the counterpulses, which are amplified regeneratively by the amplifier in such afashion that each generated counter pulse is immediately quenched.

The herein disclosed circuit may be advantageously utilized to prolongthe life of either self-quenching or non-self-quenching radiationcounter tubes. The invention will be better understood from thefollowing, more detailed description, considered together with theaccompanying single figure schematic drawing of a preferred embodimentof the invention.

The circuitry illustrated in the drawing is an abridged version ofFIGURE 3 of the parent patent, and to the extent practicable, the samereference numerals are utilized for corresponding parts.

Referring to the drawing, a radiation counter tube or Geiger-Muller tubeis designated by 48. The tube 48, when subjected to incident radiation,for example in the manner shown in the parent patent, is capable ofgenerating short duration counter pulses, but only when enabled by theaction of gate timer HQ. The gate timer normally delivers outputpotential of approximately +210 v., and this relatively high potentialnormally inhibits generation of the counter pulses by the action ofintervening circuitry described below.

The gate timer 11% generates gating pulses, such as the strikingpotential.

pulse llila to enable generation of the radiation count pulses. Such apulse a may be generated whenever it is desired to generate and countthe radiation counter pulses, for example, in a manner described in theParent patent. In the representation of the gating pulse 110a, the upperlevel is intended to be the disabling level of +210 v. and the lowerlevel corresponds to the time interval for gating the Geiger tube 48.The negative gate pulse 11th: is attenuated at the circuit junction 126by reason of the voltage division between resistors 128 and 1313, oneend of each of which is connected to the circuit junction 126 and theother ends of which are respectively connected to gate timer 11d and thenegative direct voltage source -l50 v. Moreover, the lower excursion ofthe pulse is limited to a level of -10 volts by means of the clampingdiode 132, Whose anode is tied to the junction 126 and whose cathode isat a potential of -10 volts obtained by the voltage division or" aresistor 134 connected between the l50 v. source and the cathode ofdiode 132, and of resistor 135 connected between said cathode andground.

There is also connected to the circuit junction 12-5 an end of a gridleak resistor 138 whose other end is connected to the grid 14% of anormally saturated triode 142, which serves as a combined gate, quencherand amplifier for the Geiger tube. The diagonal hatching of triode 142indicates normal saturation condition. The cathode of triode 14-2 isgrounded. Normally the potential of the circuit junction 126 is +12volts, the potential of the grid 14*!) is 0 volts, and the potential ofthe anode 144 of triode 142 is about +40 volts due to the heavy flow ofplate current from the +210 v. line through resistors M6 and 148connected therefrom to the anode 1 34. The anode 15(1 of the Geiger tube48 is conductor connected to the anode 144 of the triode 142 and istherefore also normally at a potential of about +40 volts. The cathode152 of the Geiger tube 4 8 is connected through resistor 154 to anegative direct voltage source 3l0 v. and is normally at this potential.The cathode is also signalwise coupled to the grid 14G by means of acapacitor 156.

The normal net anode to cathode potential of the Geiger tube 48 of 350volts is below the Geiger striking voltage and normally no Geiger pulsesare produced. The negative pulse 114m appearing at the junction 126 istransmitted by resistor 138 to the grid 14% and also through capacitor156 to the cathode 152, driving tube 142 to below cutoff, raising thepotential of anodes 144 and 150 to +210 volts, which appears as apositive pulse 15%;: at said anodes with a duration substantially thesame as the negative pulse lltla of the gate timer 110. Initially thecathode of the Geiger tube drops below 3l0 v., owing to the transmissionof the negative pulse through capacitor 156. This coupled with the riseof the potential of the anodes 144 and 156 to +210 volts results in ananode to cathode potential for the Geiger tube exceeding Accordingly,Geiger pulses are generated which have positive leading edges at cathode152 and negative leading edges at anode 150. Each positive cathodeGeiger pulse is transmitted from cathode 152 through capacitor 156 tothe grid and cause momentary conduction of tube 14-2 again, so that thenegative pulse at the anodes 144 and 15% due to Geiger action alone isregeueratively amplified due to the Class C amplitying action of tube142. Each Geiger pulse appears as an amplified negative pulse of about25 volts magnitude in an envelope of the positive gate pulse appearingat anodes 144 and 150, as shown at a. The 25 volt drop coupled with thecorresponding potential rise at the cathode 152 is suflicient to causemomentary quenching or extinction of the Geiger action. Upon eachextinction the anode to cathode potential of Geiger tube 48 reverts toabove striking potential and the next Geiger pulse is produced andimmediately extinguished. Alternate pulse generation and immediateextinction is repeated for the, duration of the gate pulse 11% from thegate timer 110, whereafter Geiger operation is once more inhibited withtube 142 reverting to the normal saturated condition. The pulse ofmultivibrator 98 thus serves to gate operation of the Geiger tube 48through the intervening means of triode 142 and associated circuitry andtriode 142 also serves to quench and amplify the Geiger pulses. Thenumber of Geiger pulses during the gate time interval is of coursedependent on the radiation received by the Geiger tube 48.

The Geiger pulses and their envelope are picked off from the junction ofresistors 146 and 148 and fed through a capacitor 158 to the input of apulse amplifier 160. The grid leak resistor 162 and capacitor 158connected thereto are selected to have a time constant sufiicientlyshort to filter out the envelope of the Geiger pulses while fullytransmitting the Geiger pulses themselves.

It should be understood that the aforegoing description has beenpresented by way of example and not by way of limitation, referencebeing had to the appended claims rather than the aforegoing descriptionto determine the scope of the invention.

What is claimed is:

1. In combination with a radiation counter tube having an anode and acathode, a quench circuit therefor comprising an electron tube having ananode, a cathode and a grid, a source of operating potential having atleast one high potential terminal and at least one low potentialterminal, means including resistor connecting the cathode of saidcounter tube to one of said low potential terminals, means connectingthe anode of said counter tube to one of said high potential terminalsand the anode of said electron tube to one of said high potentialterminals, said last-named means including a resistance providing a pathfor theanode currents of both of said tubes, means connecting thecathode of said electron tube to one ofrsaid low potential terminals, soas to bias said electron tube for plate current saturation whereby theanode to cathode potential of said counter tube is normally below itsstriking potential, means coupling said counter tube cathode to saidgrid and means for applying a negative gate pulse through said couplingmeans simultaneously to the grid of said electron tube and the cathodeof said counter tube thereby to cut oft the plate current of saidelectron tube and enabling generation of pulses by said counter tubemomentarily and immediately quenching each of said pulses.

2. In combination with a radiation counter tube having an anode and acathode and adapted to produce count pulses responsive to radiationincident thereupon and with voltage supply circuitry therefore, thelatter including impedance means and a circuit junction at which aregenerated voltage pulses corresponding to said count pulses when saidtube is activated, a normally inactivated amplifier having an outputterminal conductively coupled to said anode and an input terminalcoupled to said circuit junction for reception of said voltage pulses atsaid input terminal, the couplings and tube being arranged to constitutea regenerative feedback loop for said amplifier when it is activated,means for biasing the amplifier so that its output terminal is normallyat an extreme of current conduction and the tube anode-to-cathodepotential is normally below striking potential for normally inactivatingboth the tube and amplifier, and means to introduce into said feedbackloop a gating pulse eifective to drive said amplifier to an oppositeextreme of current conduction thereby to enable generation of countpulses by said counter tube, said voltage pulses being generated at saidcircuit junction, each such voltage pulse being transmitted via theinput terminal coupling to said input terminal, and in regenerativelyamplified form via the amplifier output-anode coupling so as to drivethe amplifier momentarily toward its original extreme of currentconduction to extinguish said counter tube and terminate such pulse.

References (Iited bythe Examiner UNITED STATES PATENTS 4/47 Lord 25083.6

5/56 Hamacher 25083.6

1. IN COMBUSTION WITH A RADIATION COUNTER TUBE HAVING AN ANODE AND ACATHODE, A QUENCH CIRCUIT THEREFOR COMPRISING AN ELECTRON TUBE HAVING ANANODE, A CATHODE AND A GRID, A SOURCE OF OPERATING POTENTIAL HAVING ATLEAST ONE HIGH POTENTIAL TERMINAL AND AT LEAST ONE LOW POTENTIALTERMINAL, MEANS INCLUDING RESISTOR CONNECTING THE CATHODE OF SAIDCOUNTER TUBE TO ONE OF SAID LOW POTENTIAL TERMINALS, MEANS CONNECTINGTHE ANODE OF SAID COUNTER TUBE TO ONE OF SAID HIGH POTENTIAL TERMINALSAND THE ANODE OF SAID ELECTRON TUBE TO ONE OF SAID HIGH POTENTIALTERMINALS, SAID LAST-NAMED MEANS INCLUDING A RESISTANCE PROVIDING A PATHFOR THE ANODE CURRENTS OF BOTH OF SAID TUBES, MEANS CONNECTING THECATHODE OF SAID ELECTRON TUBE TO ONE OF SAID LOW POTENTIAL TERMINALS, SOAS TO BIAS SAID ELECTRON TUBE FOR PLATE CURRENT SATURATION WHEREBY THEANODE TO CATHODE POTENTIAL OF SAID COUNTER TUBE IS NORMALLY BELOW ITSSTRIKING POTENTIAL, MEANS COUPLING SAID COUNTER TUBE CATHODE TO SAIDGRID AND MEANS FOR APPLYING A NEGATIVE GATE PULSE THROUGH SAID COUPLINGMEANS SIMULTANEOUSLY TO THE GRID OF SAID ELECTRON TUBE AND THE CATHOD OFSAID COUNTER TUBE THEREBY TO CUT OFF THE PLATE CURENT OF SAID ELECTRONTUBE AND ENABLING GENERATION OF PULSES BY SAID COUNTER TUBE MOMENTARILYAND IMMEDIATELY QUENCHING EACH OF SAID PULSES.